Snowball Earth

The Cryogenian Period: The Equator Under Ice

May 7, 2012, 6:55 pm
Content Cover Image

About 0.73 Ga, Earth underwent severe glaciations that eliminated much of life. The Cryogenian (Greek; ice + birth) period was initiated by several conditions. [1] The breakup of the supercontinent Rodinia exposed organic matter to anaerobic respiration, creating an atmosphere in which the major greenhouse gas was methane (CH4). Atmospheric CH4, in contrast with CO2, reacts with O2 and is not buffered by a massive ocean reservoir; therefore, atmospheric CH4 levels decreased rapidly once continental movements diminished and less organic matter was exposed. As CH4 declined, Earth cooled. Cooler temperatures inhibited biological production of CH4, accelerating the cooling. Ice appeared on the land masses near the equator, increasing the reflectance of solar energy (a phenomenon called albedo) and decreasing the solar energy retained at Earth’s surface. Temperatures sank until even some equatorial oceans were covered with ice. [2]

Recovery from these cold conditions depended on the buildup of atmospheric CO2 levels through volcanic emissions of CO2 and low-temperature inhibition of processes that deplete atmospheric CO2, namely, silicate rock weathering and photosynthesis. Atmospheric CO2 concentrations reached as high as 1.2% before the ice began to crack, exposing bare ground and open water, decreasing albedo, and creating a cascade of events that warmed the planet. [3]

[1] Schrag, D. P., R. A. Berner, P. F. Hoffman, and G. P. Halverson (2002b) On the initiation of a snowball Earth. Geochemistry Geophysics Geosystems 3:10.1029/2001GC000219.

[2] Pollard, D. and J. F. Kasting (2005) Snowball Earth: A thin-ice solution with flowing sea glaciers. Journal of Geophysical Research-Oceans 110:C07010, doi:10.1029/2004JC002525.

[3] Pollard, D. and J. F. Kasting (2005) Snowball Earth: A thin-ice solution with flowing sea glaciers. Journal of Geophysical Research-Oceans 110:C07010, doi:10.1029/2004JC002525.

This is an excerpt from the book Global Climate Change: Convergence of Disciplines by Dr. Arnold J. Bloom and taken from UCVerse of the University of California.

©2010 Sinauer Associates and UC Regents

Glossary

Citation

Bloom, A. (2012). The Cryogenian Period: The Equator Under Ice. Retrieved from http://www.eoearth.org/view/article/51cbf03f7896bb431f6a0e31

0 Comments

To add a comment, please Log In.